1. Field of the Invention
This invention relates to planar magnetic devices and more specifically to devices that minimize or eliminate the gap related magnetic field deformation in planar gapped magnetic structures.
2. Description of the Background of the Invention
Transformers and inductors are examples of electrical devices that transfer a magnetic or electric state from an electrified body to a proximately located non-electrified body. Many types of such devices are used in computers, telecommunications equipment, control instrumentation, and virtually all-household and commercial electronic equipment. Specifically, magnetic devices may be found as constituents of power systems, resonant filters, and electromagnetic interference (EMI) filters that shield equipment from harmful EMI and reduce EMI emissions.
The use of magnetic inductors is based on their capability to store energy. Energy is stored in a magnetic field generated by an inductor coil. The use of an inductor core permits the magnetic field to be confined and concentrated in a small volume, referred to as the magnetic xe2x80x9cgap,xe2x80x9d where the larger part of the energy is stored.
The use of magnetic devices, transformers in particular, is based on their capability to transfer energy. In many applications it is beneficial to transfer only a part of energy and store the remainder of the energy in the transformer. The use of a core in the transformer permits the magnetic field to be confined and concentrated in the core gap in a way similar to an inductor.
The magnitude and the deformation of the magnetic field generated by the inductor coil close to the gap is referred to as flux fringing around the gap. In all gapped magnetic devices, excited with an alternating current (AC), the inductor coil turns experience a high alternating magnetic field in the area close to the gap. Due to the interaction of the charge carriers and the alternating field, the resulting eddy current losses are relatively high in this area. Eddy current is an electric current induced by an alternating magnetic field.
The traditional solution, in situations where eddy currents become problematic, is the use of the Litz wire. Litz wire consists of a number of separately insulated strands twisted or bunched together such that each strand tends to take all possible positions in the cross section of the entire conductor. This design concept results in the equalizing of the flux linkages and hence reactances of the individual strands, thereby causing the current to divide uniformly between strands. The resistance ratio of the AC to the direct current (DC) then tends to approach unity, which is desirable in all high Quality Factor (Q) circuit applications.
The small wire radius of each of the Litz wire strands results in a drastic reduction of eddy current related losses. Alternatively, the DC resistivity of the coil will increase due to the application requirements. The overall benefit lies in the fact that by going to higher frequencies the required amount of stored energy, and therefore the number of magnetic inductor turns needed, may be decreased. This decreases both the over all volume and the high dissipation of energy in the winding volume close to the gap.
In planar vertically wound magnetic devices; the effects of the gap related eddy current losses have been minimized, resulting in considerably lower winding losses. The method of achieving such eddy current loss decrease, is described and claimed in a co-pending U.S. patent application Ser. No. 08/963,938, filed on Apr. 27, 1999. The disclosure of that patent application describes how shapes of components force the magnetic field close to the winding in the direction perpendicular to the plane of the component and parallel to the flat turns of the winding.
Due to the higher copper fill factor and subsequently a smaller mean turn length, achieved through the use of the foil wound components, the overall energy dissipation is lower than that found in Litz wire wound components. Still, a dissipation enhancement is found close to the inductor gap that is due to flux fringing.
Similarly, in many electronic applications of transformers, energy is stored in the gap of the transformer. A transformer is an electronic component that first transforms electric alternating current to a magnetic field and then transforms the magnetic field in to the electric current. In transformers, due to the resulting fringe fields extending outside the gap regime, eddy currents and thus high dissipation are induced in the windings around the central pole.
The object of the present invention is to minimize or to eliminate energy losses due to gap related magnetic field deformation in electrical devices such as transformers and inductors. This minimization or elimination of energy losses will result in a minimization of the AC losses and higher energy storage.
The present invention is a planar magnetic component with vertically oriented coil windings having a cross-section of a core with a torroidally-shaped winding structure taken transverse to the plane of the winding structure. The winding structure is having two adjacent xe2x80x9cwinding windowsxe2x80x9d where one or more coaxial wound coils are presented. One or more gaps in the core material surrounding the windings store most of the energy generated by the inductor. The gap of height of at least one half the height of the winding structure is confined to the area in the center of the coil-set.
Furthermore, in another aspect of the invention the gap is filled with a magnetic-polymer composite or a multi-layer structure of an alternating mono-layer comprised of equally sized ferrite particles and a layer of synthetic resin.